$7000 preamp vs $700 receiver - Is the difference THAT significant?

I'm late to the party but I want to amplify a point made above. Your desire for Macintosh gear is a complex issue. Yes, you want to make sure that you will get an improvement in sound but it's obvious that you have an emotional connection with Mac gear.

My advise is to go ahead with the Mac upgrade path - either used or new - and don't look back. Every time you listen to your system you will have a good feeling. It will not only sound better, it will absolutely improve your enjoyment of music

High end brands appeal to us in a variety of way We buy our gear for emotional reasons whether we admit it or not. A particular brand often connects with our values of beauty, value, and utility and just seems to satisfy an inner need.

If you go down a different path you will continue to lust after a Mac setup and you will always regret not following your heart.

@rabbottmke

you have gotten plenty of input here...

i would only add one more thing - you said this:

The AVR does NOT have a good DAC, as I understand it. The Bluesound has a much more evolved DAC, so I’m running unbalanced line out (relying on the Bluesound DAC) with some "TIMBRE" series Kimber interconnects.

your node 2i internal dac may be more evolved than the one in the marantz avr but as dacs go, that internal node 2i dac is not very good -- the sound is tuned to be innocuous and smooth (grey sounding) at the expense of clarity (dynamics/prat, resolution/extension, air) - so if sound quality improvement is your only priority, you should get a $1500-2000 proper hifi linestage and a $700-1000 outboard dac, and use the node 2i to feed the dac a bitstream

https://forum.audiogon.com/discussions/spend-on-the-streamer-or-on-the-dac?page=3

I wanted to suggest something else from the likes of Pass Labs, Luxman, Accuphase etc. other than Mcintosh but after reading this remark of yours

"I’d like... no, want... no, desire... to add "Blue Meters" to my setup. McIntosh haunts me. For dozens of years."

I think you better go ahead and get that dream of yours since it has been haunting you for dozens of years. Life is short, just get what you desire if it is within your financial capabilities and enjoy the finer luxuries of life. As others have aptly advised, it is true that there will be a difference. Other aspects such as matching of amp to speakers and placement of speakers in the room will be important as well.

Just to add, if the sound quality of the Mcintosh doesn't wow you too much, the high build quality will likely do. You will then realize you are getting your money's worth.

McIntosh makes really nice American gear. They use high quality components that make sense, and can be sourced around the world if needed. They’re not designed by some yahoo that will smolt exotic metal that nobody will be able to figure it out when he dies (God bless these guys). McIntosh amps stand the test of time as legacy pieces in high end market.
Perhaps if you provide some more specific information about listening preferences @stereo5 might be able to help with a more specific suggestion. He’s a knowledgeable McIntosh guy and is easy to talk to.